1. Field of the Invention
This invention relates to a monolithically integratable control circuit for switching currents through inductive load impedances coupled in a bridge circuit across two output terminals of a power amplifier.
2. Discussion of the Related Art
A control circuit for switching inductive loads coupled in a bridge configuration comprises tow power amplifiers, each comprising two interconnected stages, one stage of which is commonly called the "source" stage whereas the other stage is called the "sink" stage. The junction point between the two stages is coupled to an output terminal of the amplifier.
The load impedance is coupled in a bridge circuit between the output terminals of the two power amplifiers. The power amplifiers are switched by an input stage which, depending on the level of a logic control signal, turns on the source stage of one of the two amplifiers and simultaneously allows turning on of the sink stage of the other amplifier. The sink stage is also switched on and off by an actuating stage which switches as a function of the value of the current passing through a load impedance. When the actuating stage turns off the sink stage, a recycling diode disposed between the amplifier output and the power supply discharges the energy accumulated in the load inductance, and the source stage of the other amplifier remains turned on and continues to dissipate power.
As is known, the dissipation in power devices is high. The packages containing such devices must not only be adapted to dispose of the heat due to the high power dissipation, but must also be very small to avoid excessive cost. It is therefore extremely important to take steps to reduce the power dissipation of the aforementioned devices, at least during certain time intervals.
In a control circuit of the previously-described kind, it is particularly advantageous to limit the power dissipation of the source stage of an amplifier during the times when the sink stage of the other amplifier is turned off. To this end, there is a known method, which will be explained hereinafter in the description, for reducing the voltage drop across the source stage and thus reducing the power dissipated thereby during the aforementioned time intervals. This method, however, results in a deterioration in the operation of the control circuit, i.e. an increase in the power dissipated by the source stage when the sink stage is turned on.